[Bug regex/13637] New: incorrect match in multi-byte (non-UTF8) string

[Bug regex/13637] New: incorrect match in multi-byte (non-UTF8) string

[leonardo at ngdn dot org]

http://sourceware.org/bugzilla/show_bug.cgi?id=13637

             Bug #: 13637
           Summary: incorrect match in multi-byte (non-UTF8) string
           Product: glibc
           Version: 2.15
            Status: NEW
          Severity: normal
          Priority: P2
         Component: regex
        AssignedTo: drepper.fsp@gmail.com
        ReportedBy: leonardo@ngdn.org
    Classification: Unclassified


Created attachment 6186
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6186
reg.sh: a script to reproduce the problem

When a special string composed of single and multi-byte characters is passed to
re_search(), the function seems to lose track of which characters are
multi-byte and returns an incorrect match. This seems to be exclusive to the
ja_JP.eucjp locale.

The problem can be reproduced when the following string:

  aaa\xb7\xefa\xbf\xb7\xbd\xe8

... is matched against the pattern:

  \xb7\xbd

The two bytes in the pattern are respectively "the last byte of the second
multi-byte char" and "the first byte of the third multi-byte char" in the
original string.

The number of "a"s prefixed in the original string seems to make all the
difference here. I could only reproduce the problem when exactly 3 or 4 "a"s
are prefixed. I.e., if you remove one "a" from the prefix of the original
string:

  aa\xb7\xefa\xbf\xb7\xbd\xe8

... the problem no longer happens.

I'm attaching a script that reproduces the problem. The 'sed' version I'm using
is compiled with "--without-included-regex", so it should use glibc's regex
functions. Unfortunately I can't affirm yet that the bug is not in sed, but I'm
trying to create a self contained program to demonstrate the problem.

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[Bug regex/13637] incorrect match in multi-byte (non-UTF8) string

[sbrabec at suse dot cz]

http://sourceware.org/bugzilla/show_bug.cgi?id=13637

Stanislav Brabec <sbrabec at suse dot cz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sbrabec at suse dot cz

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[Bug regex/13637] incorrect match in multi-byte (non-UTF8) string

[sbrabec at suse dot cz]

http://sourceware.org/bugzilla/show_bug.cgi?id=13637

--- Comment #1 from Stanislav Brabec <sbrabec at suse dot cz> 2012-02-10 19:20:28 UTC ---
Created attachment 6207
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6207
glibc-regex-incomplete-char.patch

Proposed fix. There is another bug in sed that triggers infinite loop.

Description:

re_search_internal() inside switch(match_kind) in case 6 finds a possible
match. In case of our false match, verification of match not respecting
multi-byte characters fails and match_regex() returns index of such false
match.

Going deeper, re_search_internal() calls re_string_reconstruct() and that calls
re_string_skip_chars().

re_string_skip_chars() is a I18N specific function that jumps by characters up
to the indexed character. It is a multi-byte character wise function.

In case of correct run, it returns correct index to the next character to
inspect. In case of bug occurrence, __mbrtowc called from there returns -2
(incomplete multi-byte character). Why? It seems to be caused by remain_len
being equal 1, even if there is still 6 bytes to inspect
("\267\357a\277\267\275").

I believe, that remain_len is computed incorrectly:

sed-4.2.1/lib/regex_internal.c:502 re_string_skip_chars()

      remain_len = pstr->len - rawbuf_idx;

pstr->len seems to be length of the remaining part of the string, rawbuf_idx is
the index of the remaining part of the string in the original (raw) string.

I am not quite familiar with the code, but I believe that the expression should
be:
remain_len = pstr->raw_len - rawbuf_idx;


Example:

stop in the first iteration of the re_string_skip_chars()

Correct case (two leading "a" characters):
rawbuf_idx = 5
*pstr = {
  raw_mbs = 0x6479b0 "aa\267\357a\277\267\275", <incomplete sequence \350>, mbs
= 0x6479b2 "\267\357a\277\267\275", <incomplete sequence \350>, 
  wcs = 0x648190, offsets = 0x0, cur_state = {__count = 0, __value = {
      __wch = 0, __wchb = "\000\000\000"}}, raw_mbs_idx = 2, 
  valid_len = 0, valid_raw_len = 3, bufs_len = 4, cur_idx = 2, 
  raw_len = 9, len = 7, raw_stop = 9, stop = 7, tip_context = 0, 
  trans = 0x0, word_char = 0x647d88, icase = 0 '\000', 
  is_utf8 = 0 '\000', map_notascii = 0 '\000', mbs_allocated = 0 '\000', 
  offsets_needed = 0 '\000', newline_anchor = 0 '\000', 
  word_ops_used = 0 '\000', mb_cur_max = 3}

Buggy case (three leading "a" characters):
rawbuf_idx = 6
*pstr = {
  raw_mbs = 0x6479b0 "aaa\267\357a\277\267\275", <incomplete sequence \350>,
mbs = 0x6479b3 "\267\357a\277\267\275", <incomplete sequence \350>, 
  wcs = 0x648190, offsets = 0x0, cur_state = {__count = 0, __value = {
      __wch = 0, __wchb = "\000\000\000"}}, raw_mbs_idx = 3, 
  valid_len = 0, valid_raw_len = 3, bufs_len = 4, cur_idx = 2, 
  raw_len = 10, len = 7, raw_stop = 10, stop = 7, tip_context = 0, 
  trans = 0x0, word_char = 0x647d88, icase = 0 '\000', 
  is_utf8 = 0 '\000', map_notascii = 0 '\000', mbs_allocated = 0 '\000', 
  offsets_needed = 0 '\000', newline_anchor = 0 '\000', 
  word_ops_used = 0 '\000', mb_cur_max = 3}


If my observation is correct, the bug is not EUC-JP specific.

Bug triggers:
- Charset must be capable to constitute false match on the boundary of two
characters. EUC-JP fits this requirement, UTF-8 probably does not.
- There is a true ASCII match that is false match in locale specific charset.
- This false match must appear in an exact place near two thirds of the string.

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[Bug regex/13637] incorrect match in multi-byte (non-UTF8) string

[sbrabec at suse dot cz]

http://sourceware.org/bugzilla/show_bug.cgi?id=13637

--- Comment #2 from Stanislav Brabec <sbrabec at suse dot cz> 2012-02-24 20:24:38 UTC ---
Cross references:

libc-alpha mailing list:
  http://sourceware.org/ml/libc-alpha/2012-02/msg00206.html
  http://sourceware.org/ml/libc-alpha/2012-02/msg00267.html

sed+grep:
  sed: http://lists.gnu.org/archive/html/bug-gnu-utils/2012-02/msg00016.html
  sed testcase:
http://lists.gnu.org/archive/html/bug-gnu-utils/2012-02/msg00017.html
  grep: http://lists.gnu.org/archive/html/bug-gnu-utils/2012-02/msg00018.html

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[Bug regex/13637] incorrect match in multi-byte (non-UTF8) string

[sbrabec at suse dot cz]

http://sourceware.org/bugzilla/show_bug.cgi?id=13637

Stanislav Brabec <sbrabec at suse dot cz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #6207|0                           |1
        is obsolete|                            |

--- Comment #3 from Stanislav Brabec <sbrabec at suse dot cz> 2012-02-24 20:26:54 UTC ---
Created attachment 6244
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6244
glibc-regex-incomplete-char.patch

New patch with fixed ChangeLog entry and testcase.

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[Bug regex/13637] incorrect match in multi-byte (non-UTF8) string

[sbrabec at suse dot cz]

http://sourceware.org/bugzilla/show_bug.cgi?id=13637

Stanislav Brabec <sbrabec at suse dot cz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #6244|0                           |1
        is obsolete|                            |

--- Comment #4 from Stanislav Brabec <sbrabec at suse dot cz> 2012-02-27 15:13:21 UTC ---
Created attachment 6252
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6252
glibc-regex-incomplete-char.patch

Updated patch.

Changes since comment 3:
- Testcase uses test-skeleton.c.
- Uses SBC_MAX and includes "regex_internal.h".
- Setup fastmap before call to re_compile_pattern.
- bug-regex33.6 comment updated: There is one true and one false match.

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[Bug regex/13637] incorrect match in multi-byte (non-UTF8) string

[sbrabec at suse dot cz]

http://sourceware.org/bugzilla/show_bug.cgi?id=13637

Stanislav Brabec <sbrabec at suse dot cz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #5 from Stanislav Brabec <sbrabec at suse dot cz> 2012-02-28 16:42:34 UTC ---
Fixed by commit 71b5d1c (patch from the comment 4).

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